1. Field of the Invention
The present invention relates to liquid crystal displays (LCDs), and more particularly, to system for drying alignment films and a method for drying alignment films.
2. Description of the Prior Art
Recently the applications and developments of optoelectronics and semiconductor technology are increasing. Liquid crystal displays (LCDs) have been widely used in various fields of art. An LCD device comprises two glass substrates and a liquid crystal (LC) layer between the two glass substrates. Among variants of LCDs, thin film transistor liquid crystal displays (TFT-LCDs) are the mainstream.
TFT-LCD manufacturing processes are mainly divided into three parts: to form patterns on the two glass substrates, to seal LCs to form LC cells between the two glass substrates, and to package the LC cells as a liquid crystal module (LCM).
A plurality of LC cells are disposed on the glass substrates for the practical process. The number and the position of LC cells disposed on the substrates vary with the product model and the size of the substrates. The plurality of LC cells will form a single LC cell after LCs are sealed and cut.
While the LCs are sealed between the two glass substrates to form the LC cells, an alignment film is disposed on an LC cell region (or a display area, and a non-display area for the other area) of each of the glass substrates. After a rubbing process is performed on the alignment film, the alignment film disposed on the display area of the glass substrate leads to the LCs being uniformly arranged in a specific direction.
In the conventional technology, the process for forming the alignment film on the glass substrates comprises the following steps:
(1) Film coating: An alignment film material diluted with a solvent is formed on the surface of the substrates through the use of printing technology and so on. The alignment film material commonly used is polyimide. The solvent commonly used to dilute the alignment film material comprises N-methyl-2-pyrrolidone (NMP), γ-butyrolactone (GBL), and 2-butoxyethanol (BC).
(2) Drying: The solvent is evaporated at about 100° C. until a uniform alignment film is formed.
(3) Roasting: The alignment film is cured at a temperature above 180° C.
There will be two problems in the step of drying. Referring to FIG. 1, a substrate 101 is generally placed on a plurality of support pins 102. A plurality of alignment film coating areas 104 on the substrate 101 are heated by a heat plate 103. The thermal energy from the heat plate 103 is conducted to the substrate 101 through convection and thermal radiation, which slows the heating. Besides, the heating method includes heating the substrate 101 and then conducting the thermal energy from the substrate 101 to an alignment liquid on the alignment film coating areas 104, as shown in FIG. 1. So, the problems are that:
(a) In the step of drying, the plurality of alignment film coating areas 104 are not uniformly heated from the margins to the center, leading to different evaporation rates of the solvent on the plurality of alignment film coating areas 104. Accordingly, the thickness of the margins of the alignment film is not uniform, leading to the alignment ability of the margins of the alignment film differing from that of the center of the alignment film. Finally, the display operates abnormally.
(b) The substrate 101 is not heated uniformly, for the temperature of touch positions of the plurality of support pins 102 and the substrate 101 is different from that of the other area of the substrate 101. So the alignment film disposed on the plurality of support pins 102 is inclined to suffer abnormal dryness and have abnormal alignment ability, leading to a bad display quality.
In sum, whether or not the alignment liquid on the plurality of alignment coatings on the substrate is evenly heated to form an alignment film having a uniform thickness and to ensure the display effect of LCDs is one of the technical problems in LCD productions.